1. Field of the Invention
The present invention relates to a device for accelerating and storing charged particles which is used, for example, for generating synchrotron radiation.
2. Description of the Related Art
FIG. 1 shows the conventional device for accelerating and storing charged particles shown in REPORT OF THE SECOND WORKSHOP ON SYNCHROTRON RADIATION SOURCES FOR X-RAY LITHOGRAPHY, BNL 38789, INFORMAL REPORT. In the drawing, reference numeral 1 denotes bending magnets, i.e., superconductive bending magnets, which are provided with a magnetic field gradient for bending and converging a charged particle beam; reference numeral 2 denotes quadrupole electromagnets for converging a charged particle beam; reference numeral 3 denotes a high frequency accelerating cavity for accelerating charged particles; reference numeral 4 denotes a tubular vacuum duct for maintaining a revolution orbit of charged particles in a vacuum; and reference numeral 5 denotes ports for emitting radiation.
The vacuum duct 4 has two opposite linear portions and two opposite semicircular curved portions, charged particles being made to circulate therein. For example, one bending magnet 1 is disposed in each of the curved portions of the vacuum duct 4, and three quadrupole electromagnets 2 are disposed in each of the linear portions.
In this device, the beam energy is about 0.6 GeV, and typically the length of each linear portion la is 2.9 m, the distance between the respective quadrupole electromagnets 2 lb of 1.1 m, the width of the device lc is 1.7884 m, and the length of the device ld is 4.6884 m.
The operation of the device will now be described.
Although not shown in FIG. 1, two electromagnets, called a septum electromagnet and a kicker electromagnet, are interposed between the adjacent quadrupole electromagnets 2 in the linear portion for the purpose of introducing charged particles in the vacuum duct 4. The orbits of the charged particles introduced by these electromagnets are bent and converged by each of the bending magnets 1 and further converged by each of the quadrupole electromagnets 2 so as to make a stable revolution in the vacuum duct 4. The charged particles are then accelerated by the high frequency accelerating cavity 3 so that the energy thereof is increased. The intensity of the magnetic field produced by the bending magnets 1 and the quadrupole electromagnets 2 is increased in correspondence with the increase in the energy of the charged particles so that the orbit of the charged particles is kept constant. After the final energy has been attained, the intensity of the magnetic field produced by the bending magnets 1 and the quadrupole electromagnets 2 is made to be constant. Although the charged particles emit radiation from the ports 5 during passage through the bending magnets 1, thereby losing energy, this energy loss is made up in the high frequency accelerating cavity 3 so that the charged particles can continuously circulate through the vacuum duct 4 and supply radiation for a long time.
Three quadrupole electromagnets 2, which each have the function of converging charged particles, are provided in each of the linear portions of the vacuum duct 4. This is because there is no position at which the size of a charged particle beam is maximum in each of the bending magnets 1.
However, the conventional device for accelerating and storing charged particles configured as described above involves the problem that the length of each linear portion of the vacuum duct 4 is increased to some extent owing to the use of many quadrupole electromagnets 2 and further increased owing to the provision of the septum electromagnet and the kicker electromagnet which are necessary to inject the charged particles. These increases in length lead to an increase in the overall size of the device. The conventional device also involves the problem that the quadrupole electromagnets 2 are easily significantly affected by the leakage magnetic field of the bending magnets 1 because they are disposed near the bending magnets 1, and it is difficult to make a countermeasure against this.